1. Field of the Invention
The invention relates to a method of acquisition of images by X-rays, which consists in exposing the object to be visualized to X-rays and producing from these rays by means of a scintillator screen and of a charge-coupled device, electrical signals representative of the object as well as to an acquisition arrangement for performing this method.
2. Discussion of the Related Art
Image acquisition methods and arrangements of this type are already known. Indeed, upon the advent of image sensors in the form of charge-coupled devices hereinafter called CCD devices, it is possible to build photo-and-television cameras of small size which are very sensitive and usable in many fields. These devices are not only replacing the old vacuum valves as image sensors but they are at the same time imposing a digital structure to the chains of images which are using them. In the applications of images by means of X-rays, have been stated as being problems: the too small size of the sensors with respect to the size of the radiographics to be taken, the resolution less good than the conventional film and the destroying effect of the radiation upon the structure of the semi-conductor elements.
When looking into the solutions proposed in the patents EP-A-0 129,451; FR-A-2,333,404; EP-A-0 285,214; EP-A-0 372,122;; EP-A-0 373,717; EP-A-0 149,502; EP-A-0 279,294), it is found that to solve the size problem, optical systems should be called upon, which are transposing the image coming from the scintillator onto the surface of the CCD device while reducing it properly. To solve the problem of the bombardment with X-rays, the arrangement of the CCD device is based upon so as to reduce the exposed portion while going so far as to offset the CCD device at the end of an optical guide outside of the zone considered to be dangerous or screens transparent to light and sufficiently absorbing X-rays are used. The disadvantages are obvious: the price of the optical system, the geometrical distorsions, the lowering of the sensitivity and of the resolution, the non-uniformity of illumination and in particular the gauge which may be deemed inadmissible in some applications. In the field of image pick-up sensors sensing through X-rays for intra-buccal uses for instance, the best compromise until now seems to be the use as an optical system, of a frusto-pyramidal doped reducing optical fiber which operates both as an image reducer and as a screen or shield against undesired radiation.